1. Field of the Invention
This invention relates to highly insulative connector rods used to secure together multiple layers of material within a composite wall structure. In particular, the high shear strength connector rods have a high R value and are used to join together a highly insulating layer sandwiched between concrete layers on either side of the insulating layer.
2. The Relevant Technology
As new materials and compositions have been continuously developed, novel methods of synergistically combining apparently unrelated materials to form useful composites have also been developed. This is true of the area of building and construction in which high strength structural walls have been fabricated and then coated or layered with highly insulative materials having relatively low strength to provide a structure of both high strength and high insulation. In general, the structural component is built first; thereafter an insulating mat is attached to the structural component. More particularly, an outer wall structure is erected, an insulating material is placed on the inside of the outer wall structure, and an inner wall is placed over the insulating material to protect and hide it. The purpose of the insulation is to prevent, or at least slow, the transfer of thermal energy between the inner and outer walls. A commonly used measurement of the thermal insulating qualities of a material is the mathematical coefficient "R". As used in the art, the coefficient R is equal to the inverse of the coefficient "K." The coefficient K is used as a mathematical designation for the thermal conductivity of a material. Its value is determined by the molecular structure of the material, and provides a measurement of the inherent heat transference properties of the material. The coefficient R accordingly represents the inverse of conductivity, or in other words, is a measurement of the thermal resistance, or inherent quality of the insulating ability, of the material. A "high R value" material or device therefore possesses high thermal resistance or insulating ability. The outer wall generally provides the majority of the structural support of the building and will be made of a high strength material.
For example, one of the least expensive and strongest building materials that has found extensive use in the construction industry is concrete, which is formed from a mixture comprising a hydraulic cement binder, water and a relatively low cost and high compressive strength aggregate material, such as rocks, pebbles and sand. Together these form a relatively high strength, low cost building material. Unfortunately, concrete has the drawback of offering poor insulation compared to highly insulating materials such as fiberglass or polymeric foam materials. While an 8 inch slab of concrete has an R value of 0.64, a 1 inch panel of polystyrene has an R value of 5.0. However, these latter materials, while highly insulative, also have the drawback of offering little in terms of structural strength or integrity. Although structural walls made of cement or masonry can be fitted and even retrofitted with any number of insulating materials, including insulating mats or foams that are sprayed between an inner and outer wall, the insulation material is not able to impart the most efficient insulation possible due to the required structural bridging of the outer structural wall with the inner structural wall.
Such structural bridging is necessary in order for the two-wall structure to have high strength and integrity and to prevent the two walls from collapsing together or separating apart during construction and subsequent use of the building. This has usually been accomplished through the use of metal studs, bolts, or beams. However, because metal is a very good conductive material (and therefore has very low insulation), such studs, bolts, beams, or other means for structurally bridging the two walls together also create a conduit or conductive thermal bridge across which heat can readily flow, notwithstanding their being surrounded by ample amounts of an insulating material. As a result, heat can rapidly flow from a relatively warm inside wall to a colder outside wall during cold weather, for example. Therefore, although an insulating material may have a relatively high R value, the net R value of the two walls can often be far less, thus negating or minimizing the effect of adding additional layers of insulation. Of course, one might construct a building having no structural bridges between the inner and out or walls with the result being a wall having inadequate strength for most building needs.
In order to overcome these deficiencies some have attempted to pour two separate concrete slab walls with a highly insulative layer such as polystyrene foam sandwiched between the two concrete walls. For example, the following U.S. Patents disclose such a composite wall structure held together using metal tie rods or studs: U.S. Pat. Nos. 4,393,635 to Long, 4,329,821 to Long et al., 2,775,018 to McLaughlin, 2,645,929 to Jones, and 2,412,744 to Nelson. Unfortunately, as soon as metal studs or connectors are used to structurally tie together the two concrete walls, the highly insulating effect of the polystyrene foam is substantially lost due to the thermal bridging effect of the highly conductive metal studs or connectors. Thus, the polystyrene foam or other high R-value insulating material is unable to impart the full level of insulation possible because of the conductive thermal bridges.
In order to substantially overcome the problems of thermal bridging, others have begun to employ the use of tie rods having a metal portion passing through the concrete layers and a thermally insulating portion passing through the insulating layer (e.g., U.S. Pat. No. 4,545,163 to Asselin). Others have developed highly insulative connector rods that are made entirely from high R-value materials in order to connect together the two concrete structural layers while minimizing the thermal bridging effect between the outer concrete layers. For example, U.S. Pat. No. 4,829,733 to Long (hereinafter the "Long 733 Patent") discloses a plastic shear connector for forming an insulated wall having inner and outer concrete structural layers with highly insulating layers sandwiched therebetween. Although the plastic shear connector described in the Long '733 Patent has found some use in the construction industry, both the design of the connector described therein as well as the method for making such a connector create added materials, manufacturing and labor costs due to the relatively difficult method of forming the connector set forth in the Long '733 Patent, as well as the manner in which it is used.
For example, the manufacture of the Long '733 Patent connector requires at least five basic manufacturing steps, and possibly more, due to the materials used to form the connector, as well as the design of the connector. First of all, the Long '733 Patent Connector includes two separate pieces formed by different manufacturing methods and from different materials which must be fastened together to form the Long '733 Patent connector.
On the one hand, the flat, elongate portion which extends through the entire length of the Long '733 Patent connector is formed from a continuous fiber, such as glass, graphite or boron, which has been impregnated with a polyester vinyl ester epoxy or other suitable polymer binder. Although no manufacturing process for forming the flat, elongate portion is disclosed within the Long '733 Patent, the most economical and reliable method of forming a flat, elongate rod having the proper dimensions is by pultrusion. Because pultrusion (like extrusion) yields articles of uniform cross section, the flat, elongate portion must further be cut to length and then machined in order to provide the tapered portions that are necessary to retain the connector within the hardened concrete slabs. Hence, three separate manufacturing steps are required to create the flat, elongate portion alone.
In addition, the central sleeve portion must be separately molded by, for example, injection molding, and then be separately mounted over the central portion of the flat, elongate portion (column 3, lines 2-4). One of the purposes of the central sleeve portion is to provide a flange which bears on the sidewall of the insulation sheet to prevent the Long '733 Patent connector from penetrating too far or too little within the different layers of the composite wall structure (column 3, lines 4-8). Because the flat, elongate portion is formed by pultrusion, the flange of the central sleeve portion cannot be formed in one step. Thus, while providing a connector having superior insulation and strength, the Long '733 Patent only discloses a shear connector having a very highly specialized design and method of manufacture.
The Long '733 Patent also discloses a connector whose design limitations further complicate its use in the manufacture of composite wall structures. For example, the relatively wide, flat end of the connector that is to be inserted through the insulating layer and first concrete slab creates a significant amount of resistance to penetration unless the connector is carefully inserted through a hole that is pre-drilled through the insulating layer and which is significantly larger in diameter than the greatest width of the flat end of the Long '733 Patent connector.
In addition, the opposite end of the Long '733 Patent connector that is proximal to the flange has the same flat, narrow dimensions as the distal end inserted through the insulating layer and first concrete layer. Not only is the flat, narrow proximal end relatively difficult to grab by a technician attempting to force the Long '733 Patent connector through the two layers, but it does not provide a reliable surface upon which the connector can receive a strong impact or blow, such as by a hammer or mallet, to aid in the insertion of the connector through insulating and first concrete layers.
From the foregoing it is clear that what are needed are improved designs and methods for manufacturing highly insulative composite wall connectors.
In addition, what are needed are improved designs and methods for making improved connector rods that can be molded in a single step and yet provide means for anchoring the connector within the concrete layers while also providing means for positioning the connector within the insulating layer during the formation of the composite wall structure.
In particular, it would be a vast improvement in the present art to provide connector rods that could be integrally molded in one step without the need to separately mold an elongate connector shaft having means for retaining the shaft within the outer structural layers and a central sleeve portion having a flange and an enlarged central diameter for positioning the connector within the insulating layer.
In addition, what are needed are improved designs and methods for manufacturing improved connector rods that have means for facilitating their penetration through an insulating layer and a first of two structural layers during the formation of the composite wall structure.
In addition, it would be a tremendous advancement in the art to provide improved connectors having means for receiving an impact such as from a hammer or mallet, or to aid in gripping the connector, to facilitate the penetration of the connector rods through the insulating layer and the first structural layer.
Such improved designs and methods for manufacturing connector rods having the aforesaid features are set forth and claimed herein.